> I would be very interested in any pointers on how to prevent this arc tra=
cking on
> the PCB, given that preventing the initiating component failure isn't
> possible/practical.

Is it really just the PCB itself initiating the burn? In my experience it i=
s always a component failure that initiates a burn - but having said that I=
 have had a backplane PCB that had an intermittent short in it, on a minico=
mputer. But that short caused something else to give up, not the backplane.

There are reasons for component derating, and this must be one of the prime=
 ones. Also when selecting components to use only reputable manufacturers, =
especially with ceramic and tantalum caps.

>From the point of view of tantalum caps, if fireworks are a distinct hazar=
dous result, then one may be better to use the niobium caps now available. =
I believe these do not have the failure mechanisms that tantalum ones do, w=
hich result in little volcanoes'. It is hard to see from the fuzzy picture =
in the document, but I suspect the little fire they point at is actually a =
ceramic or tantalum getting red faced, and if it is a bypass cap directly c=
onnected to the coin cell, then there is probably enough current available =
to sustain it.

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